Smartcards and other secure devices are routinely used to identify personnel or provide other security features. For example, smartcards are often used to identify particular computer users, where authorized users may use a computing device or access a computing system after identification. As another example, smartcards are often used in television distribution systems, such as in cable and satellite television receivers, to control which customers receive service.
Hackers and other people routinely attempt to illicitly access secure information stored on smartcards or other secure devices. For example, fault injection is often used during attempts to identify cryptographic keys stored on smartcards. One specific type of fault injection involves manipulating clock signals in the smartcards to create glitches in the clock signals. These glitches may then lead to errors in the processes and tasks performed by the smartcards. Conventional smartcards and other secure devices often use internal clock generators with filters to filter glitches from the clock signals. However, some fault injection techniques still allow glitches to be created in clock signals, such as glitches created in clock signals transported by internal clock trees. As a result, conventional smartcards and other secure devices are still vulnerable to fault injection.